As you will see with my posting below your's, I am no plumbing expert. However, I have successfully replaced a wax ring on my toilet.

I would probably bite the bullet and replace it yourself. It takes less than an hour and it's probably less of a hassle than trying to convince the plumber that he did a bad job 5 years ago and he should do it for free.

I can't speak to your shutting off the water situation. If it doesn't turn off at the toilet, I would suggest that you shut off the main.

Replacing the wax is pretty easy, although a little messy. I did it following the instructions on the box. But there are plenty of websites that show you how. Here is a good one: http://www.hammerzone.com/archives/bath/fixt_repair/toilet/wax_ring/replace.htm

Regards,
MattC